SURVIVAL OF Bradyrhizobium japonicum IN CANADIAN PRAIRIE SOILS

The study was conducted to determine whether Bradyrhizobium japonicum can over-winter in Canadian prairie soils, and whether prolonged storage in soil exposed to various environmental conditions affects its nodulating activity. In 1984, Maple Amber, an early-maturing Canadian soybean cultivar was grown in the field on two soils that had never been contaminated with B. japonicum. Two single strains and a commercial mixture of four strains were used as inoculants. In 1985, the soils were cropped again to soybean, but the 1984 inoculated plots were split to permit noninoculated and inoculated treatments. In both years, the inoculants increased seed yield and protein content over the noninoculated treatments. Plants grown on soils inoculated in 1984, but not in 1985, had no nodules, indicating that the Rhizobia did not survive over the winter; seed yield and protein content were similar to plants grown on soils that were never inoculated. Further, the two strains of B. japonicum, 61A148 and 61A196 were more effective than the multistrain inoculant, producing more nodules and greater seed yield, but similar protein content. In the fall of 1984, soil was removed from the inoculated and noninoculated plots and subjected to storage treatments prior to cropping to inoculated soybeans in a growth chamber. Immediate cropping of soils in the growth chamber, following removal from the field, showed that Bradyrhizobia were present at the time of sampling. Prolonged storage in a frozen or severe drying condition completely destroyed the nodulating activity of the Bradyrhizobia and may have killed them; storage in a moist refrigerated state reduced their nondulating activity and may have adversely affected their survival.Key words: Glycine max (L.) Merrill, soybean, Bradyrhizobia nodulation, survival, freezing, drying